You know what? I actually don't think that RIT dye really is cheaper than jacquard. A package of RIT dye may be cheaper but it only dyes half a pound to a medium shade while a 1/2oz container of jacquard will dye 2 pounds. Take the price of the RIT dye and multiply it by 4 and then you'll get the real cost.
The RIT dye of course would be cheaper if you don't think you'd ever use all of the jacquard dye, but acid dye does keep forever, so you can always use a color then store it for months to years and you'll have it for next time.
I wrote a post about RIT a few months ago here:
RIT will work just fine on wool, but unless you have it hanging around, or want to dye right away and don't want to wait for dye to arrive in the mail, I'd suggest that you get the jacquard dye.
Edited to add:Pro Chemicalalso sells their own brand of acid dyes. The prices change by color but their smallest size is 2oz and according to them, will dye 12lbs to a medium shade.
I'm planning on buying from them soon since I'm low on dye, but I have yet to use their dyes to know if the 12 pounds really is a realistic number.